Production of rotors for electric machines



G. R. ANDERSON 2,304,067

PRODUCTION OF ROTORS FOR ELECTRIC' MACHINES Filed July 29, 19'40 5 Sheets-Sheet l I III/II] uu I/I///// I; INVENTOR. G'ORDON R. ANDERSON ATTORNEY.

942. G. R. ANDERSON 2,304Q

PRODUCTION OF ROTORS FOR ELECTRI MACHINES Filed July 29, 1940 .5 Sheets-Sheet 2 INVENTOR. GORDON R. ANDERSON ATTORNEY.

Dec. 8, 1942. G. R. ANERSON z,3o4,o67

PRODUCTION OF ROTORS FOR ELECTRIC MACHINES Filed July 29, 1940 5 Sheets-Sheet 3 /4/ 41 Lu w GORD N &A BY I GL@ z. ne@

ATI'ORNEY.

Dec. 8, 1942.

G. R. ANDERSON Filed July 29, '1940 5 Sheets-Sheefi 4 ATTORNEY.

. INVENTOR. GORDON R. ANDERSON 8, 1942. G. R. ANDERSON PRODUCTION OF ROTORS FOR ELECTRIC MACHINES Filed July 29, 1940 5 Shets-She et 5 F IG.16.

INVENTOR. GORDON R. ANDERSON M z. pa@

A'ITORNEY.

Patented 1942 2,304,067 4 PRODUCTION or across ron ELECTRIC MACBINES Gordon R. Anderson, Beioit, Wie., assinor to Fairbanks, Horse a Co., Chicago, lil., a coi-poration o! !Ilinois Application July 29, 19403845118! No. 30,093

25 Clalms. (CI. 22-65) This invention relates to rotors for electrical machines, and more particularly to a rotor member characterized by integrally formed conductor bars and end rings constituted of substantiali ly pure copper; the physical integration of the bars and end rings, or squirrel cage structure, being attained by a centrifugal casting operation. For a number of years past. various attempts have been made both in the laboratory and com mercial practice of some of the larger producers of electrical machines. to attain a rotor having relatively rigid copper windings, all of such construction that the bars and end rings are formed as an absolutely integral unit, as by casting; It is of course diilicult to attain uniform conductivity of the copper elements of a rotor structure of this type, by separately forming, and thereafter welding or otherwise metallically joining the end rings and the bars. Accordingly, the most desirable structures are those in-which the copper elements` are all cast initially as a single unit. The desiderata of all such processes is two-told. viz., first and most important, a uniform conductivity throughout the copper elements. and secondly, a uniform physical structure, avoiding bottlenecks, i. e., portions of restricted or reduced sectional area which adversely atl'ect con-c ductivity, and a physical structure such that the copper elements are intemally and externally homogeneous.

It is generally known in the art that cast copper rotors as such, have been produced more or less sporadically, but without any marked commercial success, over a period of a number of years. It is however equallyknown that none of these products has attained a commercially desirable uniformity, eitheroi'u conductivity or physical structure. such a result was not believed possible prior to the development of the process and equipment herein to be described as characterizing the present invention. !This is true in part, since there was not available, until quite recently, certain of the apparatu's necessary to produce a physically and electrically uniform product of this kind, nor was there available, within a range 'of permissive costs, copper of an initial purity to result in a rotor embodyinz fi ished cast elements of such purity as to result, not only in a high, but dependably uniform conductivity.

However, irrespective of the availability of the raw materials and development of suitable casting equipment, the developments resulting in the present process and evolved over a period oi' several years intensive experiment, have resuited in the evolution of a complete casting technique, residing in a combination of steps of processes which have been found to enable the commercial production of centrifugal cast rotors of the noted types, which for the first time, exhibit a satisfactory degree and uniformity of electrical conductivity, as well as the requisite physical characteristics.

In partial explanation of some of the points probably accounting for the commercial shortcomings of centrifugally cast copper rotors heretofore oifered to the trade, it may be noted that only relatively recently was there available as a metal for moldng, as well as containing the copper elements during spinnlng at high temperature, materials which would successfully withstand the Chemical and'mechanical eflects due to alloyin oxidation and attrition incident to any appreciable number of separate casting operations. This result has now been attained in a mold structure forming a part of the present broad program of development. Reference is made to the mold, merely as one example of improvement in materials available for practicing the process. It is further pointed out that the metal constituting the mold is desirably a nonmagnetic product. and one which undergoes no material impairment of physical strength at high temperatures, yet a material which can be machined and formed within permissive cost ranges. The metal of the mold parts must also exhibit such density and other physical characterlstics that the molten copper will not tend unduly to pick up ferrous or other contaminating impurities either by direct mecha'nical action or d'e to any surface alloying eifect. The foregoing discussion of mold requirements is herein mentioned solely by way of an example to illustrate one 'of th numerous obstacles heretofore precluding the successful commercial casting of copper. for the purpose noted, and by centrifugal methods. It may be noted further that molds of so-called rei -fractory material scarcely exhibit the requisite physical strength to withstand the stresses set up due to spinning o! the mold and contents, hence the desirability of a metal structure of more than ordinary strength and thermal resistance. i

It is by reason of a. lack of requisite casting materials in' part, and also due in part to a lack of a casting process suitable for the purpose. that there has resulted the earlier failure of any noteworthy success in the centrifugally cast rotors heretofore ofl'ered to the trade. Broadly stated,

the dimculties heretofore presented were tracedependable purity, or one characterized by not only a low percentage of impurities. but by the absence of impurities of a nature adversely affecting conductivity of the finished cast elements. Secondly, but perhaps o! equal importance, is mentioned as one of the keys of the successful commercial practice of the present process, a series of carefully conducted production steps, such that there is prevented any appreciable contamination oi the copper at any stage in the casting process, from its first melting, through to the finished cast rotor.

Accordingly an object of the invention is the Construction of a rotor having the conductor bars andend rings formed of copper and centrifugally cast in place according to an impoved method, whereby to produce an improved type of integral rotor structure.

It is an additional object of the invention to employ as the conductive metal comprising the bars and end rings in a rotor of the noted type, substantially pure or electrolytic copper for the purpose of obtaining a rotor having a highly conductive, low loss characteristic.

Yet a further object of the invention may be found in the method for centrifugally casting a pure copper rotor wherein the rotor core and mold therefor are pre-heated to a selective predetermined temperature which is coordinated with a higher pouring temperature of the molten copper, such that the fluidity of the copper is retained for the duration of the casting operation.

Another object of the invention resides in the provision for counteracting the afflnity of copper for ferrous metals, when such metals are brought into contact while at elevated temperatures, by the application of a refractory material, in the-form of an aqueous suspension, to the surfaces of the ferrous metal which are exposed to the molten copper, to provide an insulating shield thereior capable of withstanding the high temperatures involved in working with molten copper.

Still a further object of the invention contemplates the use of a suitable refractory material as an insulating medium for the purpose expressed hereinbefore, and for the further purpose of obtaining an electrical insulating film on the rotor core structure, between the magnetic core and the copper, resulting in greatly improved electrical characteristics of the finished motor.

A further object of the invention resides in the application of a thin film or coating of a refractory material to the core structure of the rotor, and to the surfaces of the casting mold therefor, so that the refractory material may assist in maintaining the requisite iluidity of the copper during the casting operation, and so that the rotor bars and end rings as cast, will be of improved and uniforin physical and electrical characteristics. y

An additional object of the invention is attained in certain improved production apparatus and equipment having particular value, either directly or indirectly, in connection 'with the improved process of ,casting of rotors of the type heretofore referred to.

Still another object of the invention is attained in the improved physical arrangement of certain of the items of production equipment, including those which of themselves, have been I 'able in part to a lack oi raw copp r of sumciently developed or improved to best advantage for the casting process.

Although appearing to best advantage in conjunction with other features of the production equipment, an important objective of the present invntion is attained in a rotatable support for the mold and contents, which presents certain marked improvements over earlier known centrifugal casting apparatus, and which is susceptible of use with or without certain of the other items of production equipment; in the broader sense, the spinning or centrlfugal apparatus includes a number of refinements such as moldlocking or holding provisions, safety features, and facilities for effecting a bodily or translatory movement of the mold and contents.

Further objects and advantages will be in part implied from, and partly pointed out in the following description oi a preferred embodiment of the present invention when taken in connection with the accompanying drawings, in which:

Fig. 1 is a perspective view of the finished rotor member which constitutes an important part of the present invention; Fig. 2 is a sectional elevation of the rotor member as seen at line 2-1 of Fig. 1; Fig. 3 is a fragmentary plan of the rotor showing the refractcry coating in the rotor bar slots as seen along line 3--3 of Fig. 2; Fig. 4 is a partial sectional elevation illustrating the steps in the assembly of the core laminations on the mold plate and arbor; Fig. 5 is a further partial sectional elevation showing the completion of the assembly of Fig. 4 and the application and extent of refractory coating required; Fig. 6 is a still further sectional illustration of the mold and core assembly showing the complete assembly and refractory coating of the mold cover and contents; Fig. 'l is a fragmentary section illustrating the extent of the refractory coating in greater detail as seen along line l-l of Fig. 6; Fig. 8 is a sectional view of the spinner mechanism and associated supporting parts, as well as a view showing the mold and protective hood in place about the spinner plate; Fig. 9 is a plan of the spinner plate illustrating the clamping jaw guide slots as seen along line 9-8 of Fig. 8; Fig. 10 is a plan view of the cam plate adapted for actuating the clamping jaws as seen along line IO-lll of Fig. 8: Fig. 11 illustrates certain details of the form and mounting provisions for the jaws as seen along line Il-ll of Fig. 8; Fig. 12 is a section through a snap-action looking pin device for looking plates of Figs. 9 and 10 from unintended e 'elative movement as seen along line IZ-IZ of Fig. 8; Fig. 13 is a diagrammatic floor layout indicating the location of the several items of apparatus and the order of steps in the process for making cast rotor members; Fig. 14 is an elevation of the mobile work table or spinner supporting member, the location of which is indicated in Fig. 13; Fig. 15 is a partial sectional elevation showing a preferred Construction of electric furnace and associated hoist apparatus, and Fig. 16 is a section through an electric melting furnace of a type herein preferred.

The desirability of employing pure copper in the Construction of electric motor rotors is evidenced by the fact that copper possesses a high electrical conductivity factor, a low coefficient of expansion for all ordinary Operating temperature conditions, sufiicient tensile strength to resist the bursting forces' created in rapidly rotating bodies, and suitable characteristics for accurate machine work. However, the production of centrifugally cast copper rotors, desirable principally because of the greatly improved electrical characteristics. has heretofore been found dimcult due to the high temperature working conditions involved, since copper must be heated to temperatures of the order of 2000" F. for reasons of proper pouring fluidity. At such high temperature, the casting mold must have adequate temperature-resisting characteristics, as well as mechanical strength, at high temperatures, to overcome centrifugal casting stresses. It is accordingly considered preferable to construct the mold parts and elements of a suitable high temprature resistant steel. However, sand or other refractory molds could be used when and if suitably adapted for centrifugal casting work.

V 3 and ease of temperature control; obviously other iurnaces may be used which are' susceptible oi' close temperature regulation. Prior to removal ot the copper i'rom the melting furnace, and pouring, the core laminations are assembled and disposed in amold of special material and construc- An important consideration in the development of a centrifugally cast rotor is the proper or necessary' temperature gradient between the molten copper and the mold and core structure within and about which the copper flows. It is obvious ,that when hot copper strikes the metal of the core and mold, if the latter is cold, the copper will freeze almost immediately. Heating the mold and core to a temperature approaching that of the copper, will materially decrease the rate of exchange of heat from the copper to the mold and core metal, and thereby reduce the rate of freezing of the molten copper. Control of the *temperatures of the copper, mold and core assembly, and consequently the rate of heat exchange therebetween, is much to be desired as the fluidity of the copper can thus be maintained until the cavitles of the core and mold are completely filled, and further, blowholes, cold chutes and 'other physical defects are eliminated. A tough, fine tion, and the mold and contents then preheated 'in a preheating furnace especially arranged for this purpose, the mold, as hereinafter more speciflcally described, being characterized by metal of a high melting point. Prior to pouring the copper into the mold and about the assembled core of the rotor, the insid surfaces of the mold which are exposed to the copper during casting, and also very importantly, the bar slots of the laminated core structure, are coated by a suitable process, later described, with a refractory and insulating material preferably in the form of a liquid or suspension such that the refractory and insulating material will adhere to the surfaces of the rotor slots and to the inside surface of the mold. With the mold and contents now suitably preheated 'and coated as described, the molten copper at a temperature of the order of 2400 degrees F., and with the mold and core at a temperature, of the order of 1400 degrees F., the equipment and mav terials are in condition for castingr The technique grain, ductile and highly conductive copper wind- A ing results from acareful control of temperature difl'erential between the copper and the mold and core, by carefully maintaining each thereof within predetermined temperature limits at the time of pouring.

In order to lead to a better understanding of the purposes of and relationships between the several preferred items of production equipment as preferably and successfully utilized in the practice of the process, the procedure will be merely briefiy described at this point.,

The procedure is initiated by the selection of a suitable quantity of pig copper; this may be in any suitable solid form such as pigs, bars or even clean copper scrap, but it is important that all of the copper constituting the melt be of at least, preferably better than commercial purity, by

' which is meant that the copper shall not contain. ,more than a trace of arsenic in any form, and

obviously not more than a trace of iron, with low total impurities. A copper of average of 99% purity is adhered to, with a variation of not more than a range of 98-99 plus percent. From this there results that there can exist in the finished cast copper elements, no electrolytical bottlenecks or poor conducting portions and from which it further results, as hereinafter more particularly pointed out, that the finished rotor castings are of dependably uniform conductivity. Electrolytic copper is preferably 'employed as a source, although the specific modeof production, whether electrolytic or smelted, is immaterial so long as just above expressed.

involved in the step of casting per se, consists,

first, in imparting a rotatng motion to the mold, and while the mold is being rotated, pouring the molten copper into the mold and into and about the core therein. This rotation is continued for a suflicient time after pouring to assure that all parts of the copper are solidified and that the copper has been brought to fill each and all of the mold and core cavities.

The range of rotational speeds for the spinning step is determined by the strength or resistance to centrifugal forces of the mold, and by the clegree of density desired in the cast copper structure. It is obvious, thereore, that the increase in size of mold will necessitate a lower speed range, and with a lower rotative speed -the uniformity of results, as to physical characteristics oi' the copper windings, becomes uncertain and undesirable. The working temperature of the mold, at the time of spinning and pouring, will determine the upper speed range When considered along with the density of' copper desired. Thus, with these several factors in mind, a range of rotative speeds from about' 1100 to 1800 R. P. M. has been selected as' the range most conducive to uniform and successful results.

After the copper elements of the rotor have been completely cast, the rotating mold and associated parts brought to rest, and the mold and contents completely restored to ambient temperature, the mold and contents are subjected -to a reheating step. For this purpose a separate reheating'furnace is employed, which may be kept at or raised to a temperature say of 900 degrees F.

- temperature, advantage of this fact is taken to The pig or bar copper of required `purity is i separate the now completely cast rotor from a mandrel element tor the like used internally of the rotor during casting, and following the latter step and a suitable cooling of the rotor, it is subjected to any necessary or desirable roughing and finishing Operations. These include, in cases where necessary, a complete removal of any excess I noted, will now copper from the periphery of the core portion of the rotor; approximate flnishing o! the end rinss, and removal ot any small amounts of excess copper which may adhere to the end laminae of the core internally of the end rings. The rcughing and g'inding steps are ing Operations as may which Operations are followed by or carried on concurrently with the steps of dynamically and statically balancing the rotor, thus putting it in condition for assembly into the frame of the machine;

In carrying out the principles of the invention as set forth above, reference will be had to the drawings, and to the following description of the rotor structure, as well as a more detailed description of the method, procedure and certain of the apparatus utilized in its production.

The completed cast rotor having a one-piece centriugally cast copper, squirrel cage structure is shown in Figs. 1 and 2, wherein the magnetic core o is comprised of peripherally slotted steel sheets or laminations ll, having a centrally located shaft aperture I: and a keyway l3, the

major elements of the rotor being completed by i the copper conductor bars |4 and end rings I5. The ender face laminations li (Fix. 2) of the core o are preferably constructed of a heavier gauge sheet metal for an obvious purpose. The refractory coating in is indicated at ll, Fig. 3. Further details of this important feature will be hereinafter noted.

The production procedure and equipment best adapted to the Construction of the rotor above be set out and described, of general principles objects course, keeping in mind the pointed out hereinbefore as well as the to be attained thereby.

The centrifugal casting operation is carried out by means of a. suitable mold structure (Fig. 6) securely clamped to and revolvably connected to a suitable spinning chuck plate mechanism and supporting structure therefor (Figs. 8 and li), the details of which will be described presently. The mold structure consists of a top mold formed to provide a tapered pouring mouth or aperture 21, a recess 22 having a slight drag or tapered peripheral wall and constituting a mold cavity for the formation of one of the rotor end rings !5, a central recess 23 for the receptlon of the stacked laminae H, and a lower end recess 24 provided to receive a bottom mold plate 25. The top mold 20 is further formed with an exterior annular groove 26 located near the bottom or open end thereof, This groove receives the jaw clamping mechanism carried by the spinning chuck plate mechanism above generally, and hereinafter more particularly referred to.

The bottom mold plate 25, received in recess 24 and held therein by frictional engagement or a slight press fit, is annularly recessed at 21 to provide a rotor end ring cavity 30 similar in all respects to the ring-formim; recess 22 of top mold 20. The peripheral land or shoulder portion 3| of mold plate 25 forms an abutment to engage the annular shoulder separating the recesses 23 and 24 of top mold 20, and also provides a perlpheral clamping means for the laminae H in cooperation with the shoulder formation between recesses 22 and 23, all as will readily appear from the drawings. A centrally apertured land or boss 32, formed on mold plate 25, forms an abutment for the central area of the stack of laminae ll. Spaced holes 23, for example three in number,

followed by final flnishbe necessary in a few cases,

the core slots of the rotor 1 i metals have the desired physical are formed in the mold plate 25, attending therethrough from the bottom face o! reeess 21, and provide vent openings for the escape o! air, ;team or vapors trapped or generated during the copper pouring process, as will be noted later.

A mandrel or arbor 33, upon which the laminae II are stacked and are keyed in non-rotative relation by means of key element 34 seated in keyway in the mandrel shank 33, is formed with a flange or projecting rib 31 which is received in a recess' 43 in the bottom face oi' mold plate 25. The seating of flange 31 in recess 43 serves to locate the mandrel shank 33, upon which the laminae I I are stacked, in proper relation to the laminae receiving recess 23 in the top mold 23. Mandrel 33 projects through the aperture in boss 32 and is keyed to the mold plate 25. as by means of key 34 which extends into the zone of the fiange 31 as shown. The upper or core-holding end of the mandrel 33 is adapted for the securement of a clamping cap element 4| as by a threaded eye bolt 42, engaging a tapped recess 43 (Fix. 4) therefore, located axialiy of the outer end of the mandrel or arbor 33. The cap 4| is suitably recessed at 44 to fit snugly over the arbor 33 and a key slot to receive the end portion o! key element 34 is provided as at 45. Cap 4| is formed to' provide a relatively wide annular beveled face 45, as shown, for the purpose of increasing the effectivethroat area of the pouring aperture 2I, as is apparent from the drawings (see Fig. 6) The slope of cap 4l also acts during pouring, to direct the stream of molten copper toward the periphery of the mold. The lower end 41 o! mandrel or arbor 33 is formed with a pair of diametrically opposed recessed flats 48, anda tapered end portion 50, as shown, whereby the arbor may be received in a clamping device, the purpose of which will be pointed out hereinafter.

suitable metals from which the above described mold parts may be made, consist of stainless steel comprised, in part, of 18 percent chromium and 3 percent nickel, and "Ni-Resist" a commercially well known high temperature nickel-steel. These characteristlcs, before` noted, and are herein preferred, though other metals may be developed or procured which will serve the same or a similar purpose. In the present case, for example, the mold parts 23 and 25 are formed of "Ni-Resist"; the arbor 33 of the s-8" stainless steel; and the key element 34,

cap 4l, and eye bolt 42 also formed of the stainless steel, above noted. These special high temperature, nonmagnetic steels have been selected, after protracted experimentation, for the reasons that the deterioration due to repeated heating and cooling is exceedingly low and as a result the repeated use of the mold parts economically Justifles the initial cost of these steels; the resistance to centrifugal stresses, while the mold parts are at high temperatures, is entirely adequate to provide a. reasonable working safety factor, and the nonmagnetic characteristic of both the "Ni- Resist" and Stainless Steel" enhances the adaptabilityof the metals to induction type furnace work. A typical analysis of the Ni-Reslst steel alloy shows the following:

Copper 5.33 per cent; chromium 3.27 percent; nickel 14.31 percent; silicon 1.62 percent; and total car-bon 3.04 percent. I

The mold parts 20 and 25, arbor 33 and laminations l I are assembled in any convenient manner or as indicated in Flg. 4. The lower mold plate 25 and arbor 33 are assembled and placed upon recess or slot for the reception o! the end 4'| of the mandrel 33. Key element 34 is positioned' in keyway 35 to lock the mandrel and plate in posi tion. A predetermined number or laminations I I,

preferably, numerically determined by weight in this case,` are next positioned on the shani: 35 of mandrel 33 such that the key 34 engages the keyway [3 of each lamination. The angular or skewed relation of the laminae, slots (Flg. 1) is obtained by forming the raised or looking face of key 34at the selected angle therefo'. This augular slot arrangement is usual practice and needs no further explanation. The heaviergauge end a work surface or support: such a support is `tically indicated at 33 and includes a fiat surface for the mold plate 25 and a central face laminations !5 are. of course, positioned to embrace the central stack of lam'inations Il. Upon completion oi the above steps, the cap 4! is pressed into position upon the end of arbor 33. and is cn'gaged by key 34 seating in key slot"45. Eye bolt 42 is then threaded into recess 43 and tightened down upon cap 4l, so that the central area of the stacked laminae is firmly compre'ssed i between cap 4| and the central land or boss 32 of mold plate 25. Theflnal assembly of these parts and elements assumes the appearance as indicated in Fig. 5. The assembled core [5, bottom mold plate 25 and arbor 33. are nowin condition to be received in the top mold member 24 (Fig. 6). However, there is an important step to be taken e before this letter assembly may be eifected. The

exposed surfaces and cavitis of both the core and mold plate assembly and the top mold, must be coated with the insulating refractory material before noted in the general discussion and oblects. The selection of a suitable refractory material is based upon !actors governed by the working temperatures involved in centrifugal casting of i molten copper, the resistance to erosiv`e and mechanical forces created by rapidly flowing molten other locations of the coating appearing in Figs. 5, 6 and 7. A similar coating 43 is applied by hand painting, spraying or in any other convenient-manneto the inside surfaces of top mold -24, and is indicated as covering the threat 2i, re-

cess 22 and core-receiving recess 23. When the refractory coating has dried sumciently, the two i major parts of the mold are assembled, 'as indicated in Fis. 6, and bottom mold plate is retained in its seating recess 24 of top mold 20, as by a press fit or by frictional engagement of the mating surfaces thereof. i

The mold and contents, now fully prepared for further Operations. is placed in a heating fumace 5| (Fig. 15) preferably of induction type as before noted, and the whole assembly raised to a temperature of the order of 1850 degrees F. The fumace loading and u loading is accomplished by providing a mold-receiving bottom opening 52 in the furnace 5! and utilizing an over-head type air hoist 53, indicated generally in Fig. 15. The Operating piunger or arm 54 of the hoist 53 passes through a fairly close fltting aperture 55 in the top of the fumace 5i, and a hoo: member 55, plvotally or swivelly attached to the lower end o! the hoist plunger. or Operating arm 54, engages V the eye bolt 42 in the end of arbor 33, thereby suspendingthe mold in a position below the openmajna .threeway-contrljhhefl in the air supplylines 55 to the hoist 53 is placed conveniently adjacent the furnace so that'the operator may control the operation of the hoist 53 to raise or lower the arm 54 and attached mold into or out metal, and insulating properties best adapted to aid in the control of the transfer of heat between masses or bodiesof diifering temperatures as well as electrical insulating properties desirably a feature in electrical rotor members zen'- erally. There are several 'possible materials whichipossess the above noted characteristics; i

notably among these is .a refractory .material known commercially as Red Bull Tale," and it is this latter material which is herein preferred.- A flnely powdered quantity of this refractory material is mixed with a ten percent solution of sodium silicate and water such that a mechanical mixture or aqueous suspension of approxi 'mately 14" Baum gravity results. This reiractory suspension was determined upon after repeated experimentation, and found to possess all of the requisite characteristics above noted.`

Since this material is not to 'any great extent a true solution, it is necessary to continually agitate the liquid in order to maintain an even consistency or density thereof.

In the handling and application of this refractor-y liquid, a tank, indicated generally in Fig. 13,

is provided and a suitable agitator is placed therein for the reason noted. The coating step in the preparation of the core and mold is eflected by dipping the' assembled core n, mold plate 25 and arbor 33 into the tank. so that the surflcial and recessed surfaces thereof receive a thin, even coat. This coating is then permitted to dry. such a refractory coating is indicated at ll; andreferred to generally in connection with Fig. 3; 75

of the urnace 5I, respectively The construction of the fumace and the arrangements for moving or lifting the mold assembly into and out of the heating chamber, are intended merely to indicate a satisfactory and preferred arrangement thereof, though other 'arrangements may be equally well adapted to accomplish the same purpose.

The placing of the mold and contents in position to be moved into'the furnace sis, in this case, a manual operation,'but the removal therefrom after heating requires special equipment which must be substantially unail'ected by the high temperatures involved, and must be' mobile and positive in its operation so as to transport the heated mold 'to the pouring station with 'a minimum of heat lossor temperature drop. as the close adjustment and maintenance of'the tem-.2

V perature gradient between the mold and contents and the molten copper is of prime importance in the achievement of a commercially successful ro- `tor member. The apparatus 'III for handling 'the work table to a pivot post 15. The pivot post 15 suitably anchored or bolted to the floor by means 'of bolts {15, is of hollow construction and the space therein is utilized to house and support the electric power lines and air supply lines for certain operating elements carried'by the wo'rl table. A cahle and pipe conduit 13, in the floor, serves to direct these lines to the floor end of the post 15.

The outer end of work table 1. is provided with a pair of parallel track members 'I'l and carried on this track is a movable carriage !I having rolling contact therewith through wheels or rollers l. (See Fig. 8.) The carriage Il supports the mold spinning and clamping mechanism which will be described in detail in connection with Figs. 8, 9 and 10. The inner end portion of work table 10 is provided with a top plate or work surface (not shown), upon which certain necessary tools and other parte may be placed so as to be accessible to the operator. The carv riage o has a depending cyindrical housing I! rigidly amxed thereto; the housing beins adapted to contain an electric motor I: and a pneumatic ram device u, these latter members constituting part of the spinning and clamping assembly for the mold and contents, later to be noted. A flexible electric power cable II extends from the motor !3 to and through the hollow pivot post li and floor conduit 'II to a suitable control station. Similarlv, air line 86 supplies air to the ram device u, control valve I'l being inserted in the line and positioned upon the frame 11, as indicated.

Referring again to the movable carriage il, it will be noted that this member is adapted to move outwardly of the end of the work table TI, so that certain. operations may be performed and carried out, as for instance, the reception of the heated mold assembly upon its discharge from the heating fumace il, and again at the pouring station where the mold is positioned and placed in condition to receive the molten copper. In each of these locations the carrisse is run out or extended so as to be in its proper position. It is necessary, therefore, to support the carriage while in its extended position, and consequently a supporting track !I is provided on the furnace supporting structure ll, as indicated in I 'ig. 15.

'The rollers Il ride onto the track members !I and thus enable the carriage !I to assume its mold receiving position beneath the furnace opening 52. similarly, the raised platform u, provided at the pouring and spinning station, is recessed or notched at a: (Figs. 13 and 14) and roller guideways or tracks u provided to receive the carriage rollers II. Carrlage ll is moved into or retracted from this extended position by means of a pneumatic ram !5, rigidly carried upon the under side of the work table 1. as indicated. The ram arm si is Secured to a push plate 91 carried at the inner end of the carriage so. Air for operating this ram is supplied thereto through pipe ss, while a line control valve 99 regulates the direction' of ram movement. The work table TI, with the carriage u in its retracted position (Fig. 14) may be manually moved through its circular orbit, or a motor or other power means may be adapted for this urpose. v

The details of the carriage II and associated parts are indicated in Fig. 8. The carriage, per se, consists of a fiat supporting surface III formed to provide, on its upper face, a rib or raised circumferential fiange III, and a central raised fiange n: adapted to the outer race of a thrust hearing IM. The carriage support consists of rollers or wheels !I mounted in supporting bracket members !05 through a shaft or axle os, clearly indicated in Fig. 8. The rollers u operate in track or guide members 11, the latter forming a part of the work table N, before noted. Operably and revolvably carried by the carriage &804,067

!I is the mold clamping and spinning organization now to be described.

A supporting sleeve lil, projecting through an aperture lil in plate ill, carries the inner raceway of hearing I". above noted. A retainer plate ll! confines the bearing I" to a limited axial movement or play. screws ll: festen plate III to the upper face of the fiange ill as shown. A second sleeve or head member IN i'its over the upper end of sleeve III, in telescoped relation, and one or more set screws il! retain these sleeves in locked relation. Slidably carried within the sleeve III is a pisten rod ill. The upper end of the rod ll! is 'enlarged. as at HQ, and this head III seats in a recess III in the sleeve IM. A packing ring !22, of suitable material, is clamped between the upper end of sleeve III and the lower face of an internal flange I!! formed on sleeve IN. screws m seat in flange m and threadedly engage the end of sleeve lll, thus retaining these elements in assembly, all as clearly indicated. The lower end of sleeve ll is fianged. as at III. and the peripheral face of this fiange !20 is suitably cut to provide gear teeth lfl. A pinion gear ill. carried on power shaft I". meshes with the toothed flange III and serves to rotate the sleeve assembly. shaft ill, suitably supported in bracket arm lil, is direct-connected to the motor u (Fig. 14) before noted. Bracket arm s is supported on the side wall of the housing u. The pisten rod !II is connected to a pisten (not shown) which operates in an air cylinder !I (Fig. 14). also contained 'in the housing II.

The sleeve I M is formed to provide an' enlarged head portion m upon which is mounted a circular spinner plate The plate m is seated in a reesa or annular notch i formedin the face of the head portion I. A series of bolts 40 or screws i" rigidly secure the plate IN in the annular notch I. A plurality of clamping members or jaw elements I, slidably carried on the 'plate m, are adapted to engage the mold assembly through the provision of the annular 20 formed intop mold member 20, before described, and shown in Fig. 6. A suitable cam plate means HI, carried in a face recess or notch III formed in head m, serves to move the clamping members I" into or out of engagement with the mold recess 28, as by a camming action between depending lugs m, integrally formed with clamps I, and grooves or channels MS, formed in the face of plate I".

The details of the spinner plate IN and cam plate I are shown in Figs. 9 and 10, respectively. The spinner plate IN (Fig. 9) is centraly apertured at !It-so that the plate will flt on the notch I!! of head member !33, before noted. A series of bolt holes are provided adjacent this aperture I for the reception of holding bolts or screws I. Three grooves or slots I are cut through the plate I and are radially directed and spaced at angles of therebetween. The clamping members ill are slidably retained in the channels i by means of an, integral; depending T shaped portion I", thedetails of which are shown clearly in Fig. il. The lugs "2, above pointed out, are carried onthe lower face of the T shaped guide members I". and project into camming grooves I in cam plate NI. As may be seen in Fig. 10, the cam plate I is formed and machined to provide spirally directed grooves m, there being as many such grooves as clamping elements I. The inner ends of grooves n are located adjacent the central aperture !48 in plate !40, and the outer ends terminate adjacent the peripheral margin of the plate, all as may be seen in Fig. 10.

In 'the assembled arrangement of spinner plate !34 and cam plate !40 upon the head !33 of sleeve member !!4 (Fig. 8), the plate !34 is rigidly secured to the head !33 by means of screws !36, while plate !40 is free to rotate relative to the head !33 and plate !34. This relative movement between the plate members is utilized 'to eflect movement of the clamps or jaw elements !38, in radially inward or outward directions.

the upper end of 'piston rod !!6, will properly i engage the bottom mold' plate 25 and press this plate into rigid engagement with the to`p mold and against the clamping jaws !38. To assist i in centering the mold assembly, the ram head !!3 and a portion of the rod !!6 are drilied out or otherwise recessed, as at !65, for the reception of the end 41 of arbor 33. This center re- This movement is transmitted to the Jaws !38 cess !55 is the preferredmeans for accurately and positively centering orlocating the mold assembly, because it is important to prevent any rotational unbalance or cit-center position of the mold and spinner plate as such an unbalanced condition may create dangerous vibrations during the spinning operation. i

The head !!3 of the air ram device 84 is further provided with slots or grooves !66, whichy cooperate with apertures 28 in mold plate to ated so that the two plates are prevented from further unintended relative movement. The looking device !50 consists of a retractible lock pin !5!, provided with a knurled'head !52 at one end, and a recess-engaging tip !53, or reduced diameter. bushing or body member !54 carried in the margin of plate !40, the bushing !54 being inserted in plate !40 from the top or upper face, as shown *in Fig. 12. The bushing or body member !54 projects below the plate !40, and a holding nut or cap member !55. is threadedly received over this' projecting end, and turned up into abutment with the bottom face of plate !40. A spring member !55, encircling the pin body !51, is retained in the space !51 between the body member !54 and cap !55. This spring acts, through abutment-with the cap !55 and a pressure pin or like member, carried by the pin !5!, to urge the pin tip !53 upwardly and into engagement with the selected one of suitably arranged recesses !!i! in the plate !34, thereby looking or preventing the plates from further unintended relative 'movement Upon disengagement of the looking pin from the plate !34,

will be positioned across the rib !63 so as to' maintain the device in retracted or unlocked position'. The spring !55 is held in compression in the body space !51 until disengagement of pin !52 from rib !53. In the present example, two such looking devices are shown (Figs. 8 and 10) but any number may be .employed. It will be noted further that the marginal portion -of the under face of plate !34 is provided with closely arranged recesses IS! so that the plates !34 and may be locked in any one of a plurality of positions, as deslred. i i

Referring again to Fig. 8, the procedure for securing and clamping the mold on the spinning plate !34 consists in, first, center-'ing the mold so that the jaw elements !38, when drawn up as before described, will each bear an equal portion of the clamping load, and so that the jaws will positively engage the groove 26 formed in the top mold member 20, and second, actuating the airam or press 34 so that the head !!9 on The pin 5! is mounted in a assist in the escape of any air or other gases which are trapped or generated during the pouring period or thereafter.

Referring to Fig.,13 of the drawings, the pre-` ferred arrangement of the several itemsof apparatus, or floor layout thereof, is indicated. In the exemplary arrangeme'nt shown, A indicates the assembly point for the core laminations mold plate 25, and mandrel-33. After the as-` sembLv, the unit is coated with'the refractory material as by dipping in a tank B. At the same time the top mold or cover 20 is internallycoated, this step being .performed at' station C. i The two major mold parts, after a period of drying, are then assembled and placed at point or station D, convenient to the heating furnaces SI.. The

worktable '!!I is .moved about its pivot post 15" so that the'outer end thereot describes acircle,

and upon this circle line are placeda battery of electric induction furnaces 5!, three being shown. The details of one such furnace are indicated somewhat diagrammatically by Fg. 15. The

pouring station or platform 32 is also located on furnaces.

of the end of work table '10. The operator takes 'a mold assembly from point D and places it in the heating furnace.

When the mold and contents reach approximately 1850 degrees F., the work table is moved to that -furnace, for example E, and when in proper position, carriage 8!! is run under th'e furnace, as by manipulation of air control valve 33, and the heated mold lowered upon the spinner plate !34. The carriage is then retracted and the work table 'moved about to the pour-ing station F, which is opposite the slot or recess 93 in platform 32. At this point F, the operator clamps jaws !38 (Fig. 8) about the mold 20, and operates air valve 81 to drive'the ram head !!9 upwardly and against mold plate 25. This latter step actsto lift the entire mold 'and contents so that any pa m the jaws !38 will be taken up. This also lifts the mold off the spinner plate !34 and provides a passage for the escape' of air and other gases forced through apertures 28 and slots !66.

Upon completion of the 'clamping and securing operation, the carriage is run outwardly 'and into 'the recess 93 so that the mold and supporting -plate are positioned, as at station G. 'At this point a hood member or safety guard !10 (Figs. 8 and 14) is lowered or placed over the mold and spinner plate assembly, as by means of an air hoist mechanism I'll; this air hoist being similar to the previously described hoist -53 (Fig 15). 'The hood !10 encloses the mold and spinner plate and comesto rest adiacent the flange "2 on carriage plate ili (Fig. 8). This complete enclosure of the rotatirg parts of the mechanism adds to the safety ,of the pouring operation, as any splashing of molten copper will be conflned to the inside of the hood I". The top surface of the hood is provided with a central aperture !12 so that the molten metal may be introduced to the mold body, positioned therebelow (Fig. 8). At the time that the hood is positioned as shown in Fig. 8, an arm or striker element !13, carried on the side of the hood makes contact with the Operating arm or lever i" of a switch ns, preferably of mercoid type, although several suitable forms of other quick acting switch will be suitable. The switch 115,

upon being actuated to circuit-closing position,

completes the circuit to the spinner drive motor 83 through a motor speed control device or resistance unit ne, as by wire ss (Fig. 13). power circuit and mercoid switch arrangement is greatly to be desired, as the moldand spinner plate cannot be rotated until the hood'or safety This to the mold and the whole is moved to the conveyor track I. The mold is then moved in the ,direction of the arrow, as by gravity or otherparts conveyed to their designated stations for guard Ilo has been properly positioned as shown in Fi g. 8.

The casting metal or copper is melted down, preferably in an induction furnace !11 of the type generally indicated by Fig. 16. The furnace crucible or lining I" is composed of a hightemperature reiractory material, such as lava or th like. The molten copper, now at a temper ature of the order of 2400 degrees F., remains in the melting furnace until use, and thereiore, to prevent oxidation, the copper is during the melting step,.deoxidized with a proper amount of silicon; thereafter, the copper is covered with a layer of charcoal na to prevent air oxidation of the hot fluid copper.

Returning now to Fig. 13, the full line showing of work table 10 at point F, indicates the mold is in position' for the casting and spinning operation. Upon positionment of the safety hood I'll, as above noted, the motor 83 is energized and the speed thereof is determined by the setting of the speed control or rheostat !15, the preferred range of speeds of spinning the mold and contents being between 1000 and 1800 R. P. M. as heretofore briefly referred to. The rotation of the spinner mechanism is commenced at a time when the temperature of the mold has been brought down approximately to 1400 degrees F. The cooling period forthe mold, .that is from the time it comes from the furnace, at a temperature of 1850 degrees F. to the time it has cooled to 1400 degrees F., provides ample opportunity for the operator to secure the mold to the spinner plate, and. to move the work table to the station G for the pouring operation, all as previously pointe'd out. Assumng that the mold temperature has reached 1400 degrees F. and rotation thereof has begun, theoperator next places a ladle, composed of graphite or lava material, in the copper melt furnace I'I'I, and dips out a suffic'ent quantity of molten copper to completely fill the mold and core cavities, This molten copper is then introduced through the hood aperture !12, and via th mold 'mouth 2! into the mold. Upon completion of the pouring step, the mold rotation is continued until the copper has completely solidified or set. The hood |10 is then removed, and carriage 80 retracted from the platform slot 93 so that work table may be moved to the discharge station H,.shown indotted Outline to the left of pivot post 15 (Fig. 13).

An overhead hoist (not shown) is then attached re-use, or to proper storage points.

The mold and core separation is carried out by subjecting the assembly to a quick heating operation in an induction furnace K, this furnace being for convenience identical with that shown in Fig. 15. This heating step produces a thermal expansicn of the mold parte relative to the core member, as by heating only the mold parts and leaving the core substantialiy unaiiected. Upon completion of this heating step in furnace K, the whole assembly is moved to suitable apparatus L, and the top mold 20 removed or presed of! of the core ll and mold plat 25. This step is followed by a second separatin operation performed upon the core H and mold plate 25. Here the mandrel is flrmly clamped in holding jaws, or other suitable means, as by the provision of jawor clamp-receiving recesses 48 formed in the end 41 of mandrel or arbor u (Fig. 6), and the core pressed or forcedfrom the arbor, as by inserting a trL-prenged tool in the apertures 28' and applying' a pressure thereto. The cast core member is then moved to'the grinding and flnishing machines (not shown) along the path indicated by arrow M, while the mold parts are returned along path N to the assembly line A for `re-use in subsequent molding operations. This above described floor layout (Fig. 13) indicates a most desirable set-up for the rapid and efllcient production of centrifugally cast copper rotor members of the type herein set forth. The items of production equipment, such as the mobile work table 10, furnaces Il. casting table or platform !2, certain of the assembly line provisions, re-heat furnace K. and Separator device L, are particularly adapted for the essential and necessary steps in the process for centrifugally casting pure copper rotor members for electrical machines. p

It may here be observed that copper rotors, specifically those for induction type motors, have been successfully produced in appreciable commercial quantitie by utilization of the method or process hereinabove described in detall. As a result of this'experience it has been found that the rotors thus produced, attain iully, each of the several objects hereinabove stated as well as many other objects implied from the ensuing description. By way of still further characterizing some of the outstandin advantages attained by the disclosed practice, it will have been observed that it is impossible, during any production stage,

v for the initially substantiaily pure copper, to be contaminated in any noticeable degree by impurities introduced in the course of casting and handling the molten metal. This condition is assured in each of the several steps throughout the whole process," for example, the copper is melted in an induction furnace of a type such as exemplified by the unit of Fig. 16 wherein the copper comes in contact with no metal other than itself, in any zone of the furnace. The molten metal, in being transferred from the furnace to the mold, is so transported in a nonmetallic ladle which prevents absolutely any metallic contamination in' this step. Again, and very importantly, in the mold itself, it has here.. toiore appeared that the mold paris are careiully and completely lined, and thus shielded to preclude any contaminating or alloying contact cifically pointed out. Thus it appears !rom the l several successive steps of the process described. as-irom the beginning oi the melting o! the copper, through the step or period wherein it is again finally and completely set or !rozen in the flnished product, that the copper i carefully kept rrom any metallic alloying influence.

From the toregoing it will become apparent that there are prevented (a) any iusion o! the copper to the steel or to the metal mold surfaces, and also prevented (b) any pickup by the copper of iron or other metaiiic impurities when the copper is poured into the mold or assembly and while it remains in fluid state during at least the earlier part oi' the centrifugal spinning stage.

In order still further to distinguish the present process and the product' obtained, from those characterizing the earlier attempts at centrifugal casting of comparable products it may be noted that such eariier and unsuccessful experience in centrifugal casting of contacting copper elements has resulted in a wide and 'uncontrolled degree oi variation in conductivity oi! the resulting copper elements. To illustrate actual experience, by the older process, the maximum conductivity obtainable never exceeded '70% and conductivities often as low as 40% were encountered. It is herein noted that the percentage conductivity values herein referred to are given. with reference to the more or less theoretically 100% conductivity obtainable with chemically pure copper. It is noted now after an extensive experience with the aforementioned process and product, that (a) it is now possible for the first time dependablyto obtain any desired conductivity in rotor after rotor, on

a production basis. with but inconsequential variations. Furthermore, this susceptibiiity of, accurately controlled conductivity prevails with a. further new result (b) in having dependably raised the maximum conductivity up to 'at least the value oi' 90%. These results are due in large measure to the fact of the several described steps for preventing pickup of ferrous impurities in any stage of the process, it being noted that only a raction oi a single percent oi' 'iron in solution with the copper, creates a marked difference in conductivity.

It is to be understood that the foregoing ex- 'plicit disclosure is intended solely to teach a preferred method, and to indicate desirable and satisfactory equipment, tools, -and other apparatus for carrying into efiect theproduction of a substantially pure centrifugally cast copper rotor member. However, numerous changes and alterations may be eilected in the methods and equipment therefor without materially departing from the final results to be obtained, or without departing from the spirit and intended scope of core to a degree to stabilize and integrate the rei'ractory. in coating a metal mold element with a refractory, heating the coated mold element to render the refractory thereon, substantially impervious, positioning the mold element and core in assembly for casting, .in rotating the core, in admitting substantially pure molten copper to the core slots-during core rotation, and in continuing rotation oi the core until solidiflcation of the copper in the core slots.

2. The described method of casting the copper winding elements in a core i'or an element of an electric machine, which consists in surfacetreating the winding seats of the core, and the internal surface of a mold, with a refractory, heating the core and mold to integrate the ref-actory. surrounding the core with the mold, pouring molten copper oi' a minimum purity of 98%, and at a temperature of the order of 2400 F., into the mold containing the rotor core, pouring'the molten copper while the mold is being rotated at a substantial speed, and continuing the rotation oi' the mold and contents until the metal is substantially frozen. i 3. The described method oi casting, as an integral unit, the copper winding elements of a rotor for an electric machine, which consists in iorming a .barrier oi' non-ierrous material in the winding seats oi the rotojorming a similar barrier on the inti'ior mold surfaces, pouring into the mold, molten copper of a minimum purlty of 98% at a temperature substantially above the meiting point of the copper, maintaining the mold at the time of beginning pouring oi' the metal, at a temperature of the order of 1300-1500 F., rotating the mold at a substantial speed through the pouring step, and continuing rotation of the mold at least until completion of the step o! pouring the copper.

4. The described method of casting as an integrai unit, the copper winding elements of a rotor for an electric machine, which consists in applying a retractory coating to the rotor as a base for the winding elements, applying a lining of a reiractory to the innermold surfaces, pouring a metal which is essentially a 'substantialiy pure molten copper into the mold containing the rotor core. and while the metal is at a temperature of the order of,200e-2500 F., heating the mold to a temperature, at the time of beginning pouring, of the order of 1300-1500'F., and pouring the molten copper into the mold while the mold is being rotated at a substantial speed, thereatter continuing the rotation of the mold and contents at least until the completion of the pouring step.

5. The described method of casting as an integral unit, the copper winding elements of a rotor for an electric machine, which consists in pouring molten copper oi' a minimum purity of 98%, into a mold containing the rotor core or equivalent winding support, coating and thermally integrating a refractory surface covering on the winding support and internal mold surfaces, pouring the molten copper while the mold is being rotated at a speed within the range of 800-1800 R. P. M., and continuing rotation of the mold and contents at least until the molten metal is completely introduced to the mold.

6. The described method ot casting the copper windings ot one element of an electric machine, which consists in pouring molten iron-free copper into a spinning mold containing a support for the windings, adhesively lining the mold with oi a slotted core, in heating the rei'ractory coated a non-ferrous reiractory adhesively coating with a reiractory. the surtaces oi the support to be engaged by the windinss, and spinning the mold substantially until the copper !oi-mins the wind- 'copper for pouring, in a second container provided with a non-ferrous surface engaged by the molten copper, adhesively lining a mold with a reiractory material of insulating characteristics, coating the suriaces oi a winding support with an integrated insulating barrier to engage the windings. pour-ing the copper into the mold and spinning the mold while pouring, and in homogenizing the metal by continuing the rotation oi the mold until the copper therein is substantially rrezen.

8. The described method of casting copper windings for one element oi an electric machine including a core, the 'nethod including the steps oi melting by inductively heating, a substantially iron-free copper, lining the mold and coating the core suriaces within the mold, with a silicate reiractory and adhesively securing said reiractory to the interiorly exposed mold suriaces, rapidly rotating the mold and contents, pour-ing the copper into the mold during rotation, continuing rotation of the mold until substantial ireezing o! the copper, inductively reheating the mold and contents only to the point oi loosening the cast windings and core rrom the mold, and removing the contents of the mold.

9. The herein described method oi iorming a bi-metallic winding and core element tor an electric machine, which consists in surrounding a substantially assembled core structure by a mold, admitting to the mold a molten conducting metal which consists essentiaily of copper, coniining said metal substantially throughout the mold cavities by a wall ci a refractory material, and rotating the core and mold at a substantial speed at least until the mold `cavities are iilled with the conducting metal.

10. The herein described method of rorming a aso-1,067

prior to the introduction ot the molten metal to the core, and continuing such rotation at a suhstantial speed, at least until the core cavitiu are substantially filled with the molten metal.

12. The described method of iorming a rotor or like unit !or an electric machine, the unit being of a type characterized by a core with cast-in conductor bars and end rinas, which consist in substantially assembling the core structure provided with peripheral bar-receiying slots. formin: a substantialiy impervious lining within mold structure over the portions thereo! to be eng led by the conducting metal in casting. suhstantllly evenly coating the bar-receiving portions of the core and winding structure for an electric machine, which structure is of a type characterized by conducting elements cast into the core, the method consisting in surrounding a substantially assembled core structure by a mold, forming a metal-engaging surface interiorly of the mold which is substantially impervious to the molten conducting metal, iorming on those portions of the core structure to be engaged by the molten casting metal, a substantialy impervious coating of a refractory material, admitting to the mold and core a molten conducting metal which consists essentially of copper. and rotating the mold with the core therein, at a substantia s'peed until the conducting-metal-receiving cavities within the mold are substantially filled with the molten conducting metal.

11. The described method oi forming a core and winding structure for an electric machine, which structure is of a type characterized by cast conductor bars and end rings cast integrally with said bars, the method consisting in erecting a sealing barrier of a reiractory material perlpherally of the assembled core structure of the rotor, forming a barrier of a similar material in the barreceiving portions of the core, thereaiter admitting to the mold a casting metal consisting essentially oi copper, rotating the barrier and core core structure, with a reiractory material, introducing to said portions a molten conducting metal containing copper in substantial amount and o! a degree of purity to assure uniiorm conductivity, and rotating the core and mold at a substntial speed, at least from the time of beginning of pouring of the molten conducting metal, until the oonducting metal cavities within the core and mold are substantially filled.

13. The described method of producing a rotor or lik unit for an electric machine by a centruugal casting process, which consists in building up a laminated core portion of the unit, characterized by peripheral bar-receiving slots, forming in each of said slots a scaling barrier of a material refractory in nature and virtually unaflected by contact with the molten conducting metal, iorming a sealing barrier o! a similar material in a manner substantially to coniine a molten metal to spaces peripherally within the circumierential portions of the core, and to spaces endwise thereof to form the end rings, admitting to the mold a molten conducting metal which consists essentialy of copper, and spinning the core and mold beginning at least with the time o! introduction of the molten metal thereto, and continuing until the cavities of the mold and core are substantially filled with the conducting metal..

14. The described method of forming for an electric machine. a rotor or like unit of a type in which the conducting elements are cast as a single Physical unit, in place in and on a core, the method consisting in applying to the core portions to be engaged by the cast metal, a barrier o! refractory material, thereatter heating the core and thereby eflecting at least a slight phase change in said refractory barrier, iorming on the inner surfaces o! a mold to contain the core during casting, a refractory barrier, heating the mold prior to casting, to an extent to cause the refractory thereon to undergo at least a slight phase change. introducing the reractory-treated core strnctm-e to the refractory-treated mold structure, admitting to the mold and to cavities within the core. a molten conducting metal which consists ementialy of copper, and spinning the mold and core at least throughout the time of admission thereto of the molten conducting metal.

15. The described method of orming a rotor or like unit characterized by cast eonduting elements, for use in an electric machine, which consists in the several steps as recited by the preceding claim and further characterized in that the refractory-treated portions of the mold are iso- &soccer ing metal, to nn ex i of taic barrier io. In 'the describ or like unit choir& nichts, and odepted ir in an eieetrc machine the step, practiced distnetiy pris:: 'to coming the casting matches? et ieast surficieily, e re iraciery en those surrat-es of o imiitup rotor core, to be engaged by the cest conducting elements of the core. y i

17. In 'the described process oi orming e. rotor or iike unit eharecterized by a core and integrsliy cast oonductrg elements thereon, and adapted for use in an Electric machine, the step which consist in eppyng a reractory material to those portion:: of a. builtup core adapted to engage the ccnducting elements, heating the core and re iractory, prior to casting, to an extent cheating at least surficial 'usion of the rei'ractory, and in heating, Drier to pouring the cast conduoting metal, a reiractory surface of a mold for use about the rotor to an extent to ficct at least surficial usion of a refractory portion to be engaged by the molten conducting metal.

18. The described method of casting Copper windings for one element of an electric machine including a core, the method including the steps of meiting by heating, a substantially iron-tree copper, lining the moid'and costine the core surfaces within the mold, with a silicate refractory and adhesively securing said refractory to the interiorly exposed mold suri'aces, rapidly rotating the mold and contents, pouring the copper into the mold during rotation, continuing rotation of the mold until substantial freezing of the copper, rehe ating the mold and contents only to the point of ioosening the cast windings and core from the mold, and removing the contents of the mold.

19. The method of casting copper windings in the rotor member of an electric machine,.which :omprises the steps of coating the faces .and slots f a. rotor core and the adjacent surfaces of a. mold containing the corewth a refractory ma- ;erial composed essentially of a. silicate of magesium, heating the moldand contents through l temperature range of the order of 1300-1900 E'., thereby causing partia! sintering of the refrac- ;ory, admitting substantially pure molten copper ;o the mold, while the mold is' at a temperature within the lower temperature range, and contin ously rotating the heated mold and contents ini-ing the pouring oi' the molten copper and un- ;il substantial solidification' oi' the copper mass.

, 'or ;mold sui-faces. ooess of iorming e, tetor .east oonduoting ele- 20. In the described process oifo'ming an eler nent for an electric machine, which element is f a type characterized by cast conducting windngs seated on a supporting core therei'or, the tp which consists, after pouring and freezing i' .the casting metal but while theclement renains in with a. mold element in reestinz the mold element to a temperature within "a muze substntialy below that ot the stantially until the copper formin: the conductneitin: point oi' the cast conducting metal wherey to expsnd the mold element away from the :ast conductinz elements and releasing the mold From-the cast core structure. A l i 21. In tbe,method of ;ox-min: a. bi-metallic -otor charscterized by a peripheraily siotted core nd integrslly cast conducting elements thei-con,

rle steps which consist in applylng a retractory material to the suraces of the rotor coreend Slots, introducing the ref'actory-coated core 'to a mold ormed to provide oavities at both ends of the rotor thei-ein iusing the refractory on the sui-faces and in the siots of the core, murin# molten casting metal endwise into the cevztes of forming in each of the Slots a scaling barrier of a refractory material, fusing the refrac'tory material within the siots so that it is virtuaiiy unafiected by contact with the molten bar-form ing casting metai, and pouring the moiten cast ing metal into the slots, endwise thereoi, so that a. portion of the casting metal is extruded through the restricted portion of each oi' the slots to protect the bar-forming metal within the slots from contamination by the core metal.

23. The described method of casting a struo tural unit for electrical apparatus, which unit is of a type embodying a recessed body of a. ferrous metal and other parts of spaced, cast, conducting elements occupying recessed portions of the body, which method consists in applying a thin coating of e. refractory material to the surfaces and recesses of the body, in heating the refractory coated body to a. degree to stabilize and integrate the refractory, in coating a metal mold element. with a. rfractory, heating the coated mold element to render the refractory thereon substantially impervious, v positioning the mold element and body in assembly for casting, in rotating the body, in admitting a substantially pure conducting metal to the body recesses during rotation, and in continuing rotation oi' the body until solidiflcation of the conducting metal in the recesses. i e 24. 'I'he described method of casting a 'structul-al unit for electrical apparatus, in which aportion of the unit consists of spaced, cast, conducting elements, which method consists in pouring molten iron-free copper into a spinning mold containing a support for the conducting elements, adhesively linin: the mold with a. non-rerrous reimctory, adhesively coating with a refractory the surfaces of the 'support to be engaged by the conducting elements, and spinning the mold subing elements, is !rozen throughout its mass.

25. The described method of'castingi a structumi unit for electrical apparatus, in which I.

portion of the 'unit consists oi' spaced, cast, conducting elements', which method consists in surrounding a substantiallynssembledcore structure by a mold, admitting 'to the mold s molten conducting metal which consists essentially o! cop 

